In crop farming industry, controlling weeds which restrain the growth of crops and reduce yield and protecting crops are very important. In order to reduce the loss caused by weeds during crop cultivation, such as poor growth or reclined crop yield, some herbicidal active components have been developed to control weeds effectively while remain safe to crops. By far, there are a large number of developed herbicides have been registered and applied to control some weeds growing in crops. The herbicides which are applied to control weeds in specific crop cultivation should possess an effective level of herbicidal activity and broad-spectrum of weed control, as well as be safe enough to environment and crops. However, not all of them can fully comply with aforesaid requirements.
The traditional method of enhancing herbicidal activity and broadening herbicidal spectrum of existing herbicides is to mix two or more herbicidal substances with different herbicidal activity. When the efficacy of a mixture with two or more ingredients exceeds the anticipated efficacy of each ingredient, it is called “synergistic effects”; when the efficacy of a mixture with two or more ingredients is beneath the anticipated efficacy of each ingredient, it is called “antagonistic effects”; when the efficacy of a mixture with two or more ingredients is equal to the anticipated efficacy of each ingredient, it is called “additive effects”. However, as a result of the difference in herbicidal efficacy, absorption rate, transmission and metabolism, the herbicidal activity of most mixtures is lower than that of each ingredient applied separately. Only under certain circumstances, the herbicidal mixture exhibits synergistic effects when two or more substances with herbicidal activity are mixed together.
Pyroxasulfone, with chemical name as 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl) pyrazol-4-ylmethyl sulfonyl]-4,5-dihydro-5,5-dimthyl-1,2-oxazole, is represented by the following chemical structure:

Pyroxasulfone was described in EP1364946 and US20050256004. Although Pyroxasulfone is a highly effective pre-emergence herbicide, its activity becomes low after the emergence. When Pyroxasulfone is applied to certain dicotyledonous crops, such as cotton, sunflower, soybean, and brassica crops, such as canola and oil rape and some gramineous crops, such as rice, wheat, rye and barley, the crops may suffer from unacceptable level of harms.
It is known that by applying the mixture of some different herbicides having specific effects can enhance the activity of herbicidal ingredients which is more effective than simply combining them. This activity enhancement is also called synergistic effect or synergistic activity and thus it can decrease the application rate of herbicidal active compounds used to control harmful plants.
Topramezone, with chemical name as [3-(4,5-dihydro-3-isoxazolyl)-2-methyl-4-(methylsulfonyl)phenyl](5-hydroxy-1-methyl-1H-pyrazol-4-yl)methanone is represented by the following chemical structure:

Topramezone is a new type of herbicides in inhibiting hydroxyphenylpyruvate dioxygenase enzyme. Topramezone and its preparation have been disclosed in WO98/31681 and WO99/58509. Its mechanism involves inhibiting 4-hydroxyphenylpyruvate dioxygenase (HPPD) enzyme in the biosynthesis of plastoquinone, so that indirectly affecting the synthesis of carotenoid pigment and disrupting the synthesis and function of chloroplast in the presence of light, resulting in severe chlorosis and etiolation, dead tissue and plant death at 14 days after the treatment. It is absorbed through foliage and roots of the sensitive weeds by bidirectional (upward and downward) transmission inside the plants which stop growing soon. After 2-5 days of application, the weeds above the ground show symptom of etiolating and poisoning, particularly at the areas of growing point, blades and leaf vein. These etiolated tissues gradually die and the whole plants die within 10-15 days according to weather condition. Topramezone is safe to corn, as different from sensitive weeds, the herbicide resistance of corn is achieved by lower sensitive to target enzyme, less uptake and transmission and faster metabolism. Topramezone is able to effectively eliminate annual gramineous weeds and sedge weeds, such as Common crabgrass, Barnyardgrass, Setaria viridis, Brachiaria eruciformis, Eleusine indica, Wild Panicgrass, fountaingrass, Cenchrus, Cyperus difformis, Cyperus iria, Amaranth, knotweed, bindweed, thistle, pigweed, cocklebur, Solanum nigrum, Abutilon, Datura stramonium, Galeopsis, Matricaria recutita, Ambrosia, Sinapis arvensis, Daucus carota, Acanthospermum, Acanthospermum hispidum, Mercurialis Annua, Desmodium tortuosum, Emilia sonchifolia, Galinsoga parviflora, Nicandra physalodes (Linn.) Gaertner, Common Dayflower, Lindernia crustacea (L.) F. muell and Mazus pumilus. Topramezone is also capable of controlling those broadleaf weeds that appear resistance to ALS and triazine herbicide effectively and steadily.
Atrazine, with chemical name as 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine, is represented by following structure:

Atrazine is a systemic selective herbicide used at pre- and post-emergence stage. Atrazine is absorbed most readily by plant roots, rarely by stem and leaf and it is able to control weed by soil sealing and at early post-emergence, effective in controlling annual broadleaf weeds and gramineous weeds. Atrazine is prone to be moved to deep layer of soil by rainfall, therefore it is effective to certain weeds root deeply, but it is easy to produce toxic substance. As persistence of Atrazine in soil is very long, it is not recommended to increase its application rate randomly, especially in the arid areas, in case to cause harms to post-harvest crops.
In the current, the herbicide spectrum is limited because of regulation to ensure the safety of crops. Application of a single herbicide is unable to completely and effectively control the weeds in the field of crops, on the other side, over-dosed herbicide or unevenly application is likely to produce unacceptable toxic to current crops or post-harvest crops. Pyroxasulfone is a highly effective herbicide used before emergence, but becomes less active after the emergence stage. Besides, the compatibility of Pyroxasulfone with some dicotyledonous crops, such as cotton, sunflower and beans, brassica crops, such as canola and oil rape, and certain gramineous crops, such as rice, wheat, rye and barley, is not ideal, as it not only damages the target plants, but also harms crops at unacceptable level. In principle, the damage to crops can be eased by decreasing the application rate, while its efficacy of control target plants also reduced accordingly.